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Is there a mode in which a Kinetis MKM34Z256 drives RESET Pin active after Power up (POR)?

Question asked by Manfred Eggersdorf on Aug 29, 2017
Latest reply on Sep 7, 2017 by Hui_Ma


I have got a problem in the 3rd revision of scematic/layot which I do not understand.

When I take the new unprogrammed PCB's and power up (POR) - then I can't program it.

So I looked at the RESET-Pin - and this got a voltage of 390mV.

The RESET Pin is normally Pulled up with a 470R Resistor.

If I connect the RESET Pin direct to 3.3V - a current of approx 30mA is measurable - so it looks llike the Reset drives as an Output.

I tried with different PCBs - same behaviour.

So does anybody has a idea what could be?


Best Regards




Some measurements later...

The RESET Pin of the uC is driven low by the Kinetis itself for some microseconds - then released - then driven low again - and so on...

It looks like a Pulse Width Modulation with a frequenc of approx 3 kHz.

What could be a reason for this behavior?


Best Regards Manfred